This invention relates to hydraulic valve control systems, and more particularly, to hydraulic control systems having a valve mechanism for controlling the engagement and disengagement of a torque transmitting friction device. Specifically, this invention relates to such systems wherein the friction device has a time-pressure relationship during engagement.
During the engagement of a fluid operated torque transmitting device, such as a clutch or brake, it is desirable to provide an engagement signal having a rapid fill portion and a controlled pressuring portion. This is generally accomplished by combining one or more valves with an accumulator in a friction device fill circuit. The fill time and pressure is generally determined by the minimum spring load on the accumulator or the minimum spring load plus any accumulator bias pressure that is present and the volume of the apply chamber for the friction device.
The pressuring or pressure rise portion is controlled by the spring rate in the accumulator plus any variable bias pressures that might be present. These systems require at least a shift valve and an accumulator. Some systems also require control valving for the accumulator. The prior art mechanisms require space and therefore add to the size and weight of the system. Also, in these systems, the machining complexity and added structures contribute to the overall cost of the system.